Dock levelers or dockboards, as they are also called, are adapted for installation adjacent loading docks to span the gap between the dock and the floor or bed of a truck. Dockboards of this type have a ramp or deck which is hingedly mounted at its rear edge, the front edge of the ramp having an extension plate hinged thereto for engagement with the bed of the truck. The entire dockboard is normally positioned within a shallow pit near the loading edge of the dock so that the rear hinged edge of the ramp is flush with the top of the dock, the ramp normally being maintained in this flush position when not in use. However, when in use, the ramp may be angularly inclined upwardly or downwardly to accommodate different bed heights and vertical movement of the bed during loading or unloading.
The structure and operation of such dockboards are well known, and several typical such dockboards are disclosed in U.S. Pat. Nos. 3,835,497; 3,882,563; 3,921,241 and 4,126,909, all owned by the assignee of this application.
To use the dockboard, the truck to be unloaded or loaded is backed into position adjacent the front of the dockboard, the rear edge of the bed being adjacent but slightly spaced from the dock by bumper pads. The hold-down device of the dockboard is then released so that the front edge of the ramp is raised upwardly, as by springs. This upward swinging of the ramp also causes the extension lip after it has cleared the rear end of the truck bed, to be raised. The operator then walks out onto the ramp to lower it, thereby causing the extension lip to move downwardly into engagement with the truck bed. The ramp, with its extension lip, thus bridges the gap between the dock and the truck bed, even though the truck bed may be above or below the dock level. A hold-down device normally prevents the ramp from lifting off the truck bed, although this device is designed so that the front edge of the ramp can float up and down with the changing height of the bed as the loading or unloading proceeds.
To support the ramp in a generally horizontal or cross-traffic position wherein the ramp is flush with the dock, such as when the dockboard is not in use with a truck, it has been conventional to provide a cross-traffic support associated with the ramp. This support typically comprises cross-traffic legs hingedly suspended from the ramp adjacent the forward edge thereof, which legs are disposed for engagement with fixed stops provided on the dockboard frame. Various forms and variations of such cross-traffic legs have been utilized, as disclosed in U.S. Pat. Nos. 3,921,241; 3,902,213; 3,877,102; 3,858,264 and 3,137,017. While many of these known arrangements have operated in a satisfactory manner under selected operational conditions, nevertheless most of the known cross-traffic leg arrangements have possessed recognized operational disadvantages, and/or have been undesirably complex both structurally and functionally.
The present invention thus relates to an improved cross-traffic support structure for a dockboard which is believed to overcome some of the disadvantages associated with the known structures, particularly under selected operating conditions, with the improved cross-traffic support structure of this invention possessing advantageous and improved structural and operational features.
More specifically, the present invention relates to a dockboard having movable cross-traffic legs associated therewith, and a latch mechanism which automatically engages and holds the cross-traffic legs in a retracted or inactive position when the dockboard is being actively utilized for loading or unloading a truck, which latch mechanism is automatically unlatched following removal of the truck bed from beneath the ramp so that the legs are automatically returned to their active position for supporting the ramp flush with the dock.
In the dockboard of the present invention, once the legs are latched rearwardly, they will remain latched while the dockboard is being used, whereby the legs do not interfere with the ability of the ramp to pivotally float up and down with the truck bed as loads are removed therefrom. This is particularly desirable since, during the unloading of a truck, as by means of a fork lift, the removal of the load coupled with the repetitive movement of the fork lift onto and off the truck bed causes the bed to float up and down several inches. If the cross-traffic legs are positioned for engagement with the stops during this unloading operation, the cross-traffic legs can prevent the desired lowering of the ramp when the bed is lowered, whereby the lip plate pivots downwardly so as to remain in engagement with the truck bed. This results in the lip plate creating a rather steep grade which makes it difficult for the loaded fork lift to exit from the truck. The latch mechanism of the present invention prevents the cross-traffic legs from engaging the stops during this type of operation, thereby insuring that the ramp will properly vertically float in response to weight-induced elevational changes of the truck bed.
According to the present invention, there is provided a dockboard having a hinged ramp positioned for engagement with the bed of a truck, which ramp is freely swingable through a selected angle which extends both above and below a horizontal position to thereby accommodate various bed heights. Cross-traffic legs are swingably mounted between the ramp and abutments so as to maintain the ramp at dock level for cross-traffic purposes, such as when the dockboard is not being utilized for loading or unloading a truck. The ramp has a lip pivotally supported at the front edge thereof, which lip is maintained in a downwardly suspended or pendent inactive position, the lip being actuated by a conventional mechanism when the ramp is elevated so as to lift the lip into a position wherein it is substantially flush with the ramp. A latch mechanism is provided for latching the cross-traffic legs in a rearward inactive position, this latch mechanism being automatically activated for latching the legs in response to upward lifting of the ramp during extension or raising of the lip. When so latched, the cross-traffic legs are no longer engageable with their abutments during normal utilization of the ramp. However, when the ramp reaches its lowermost position, the latch mechanism is automatically released so as to unlatch the cross-traffic legs so that they may resume engagement with the abutments when the ramp is returned to a position wherein it is level or flush with the dock. A manually-actuated retracting mechanism is also connected to the legs to enable them to be drawn rearwardly into their inactive position, without resulting in latching of the legs or requiring raising of the ramp, so that the ramp can be dropped downwardly below its dock-level position while maintaining the lip in its pendent position.
Other objects and purposes of the invention will be apparent to persons familiar with dockboards upon reading the following specification and inspecting the accompanying drawings.